Evaluating the Impact of Florida’s “Stand Your Ground” Self-defense Law on Homicide and Suicide by Firearm: An Interrupted Time Series Study

Importance In 2005, Florida amended its self-defense laws to provide legal immunity to individuals using lethal force in self-defense. The enactment of “stand your ground” laws in the United States has been controversial and their effect on rates of homicide and homicide by firearm is uncertain. Objective To estimate the impact of Florida’s stand your ground law on rates of homicide and homicide by firearm. Design, Setting, and Participants Using an interrupted time series design, we analyzed monthly rates of homicide and homicide by firearm in Florida between 1999 and 2014. Data were collected from the Wide-ranging Online Data for Epidemiologic Research (WONDER) web portal at the Centers for Disease Control and Prevention. We used seasonally adjusted segmented Poisson regression models to assess whether the onset of the law was associated with changes in the underlying trends for homicide and homicide by firearm in Florida. We also assessed the association using comparison states without stand your ground laws (New York, New Jersey, Ohio, and Virginia) and control outcomes (all suicides and suicides by firearm in Florida). October 1, 2005, the effective date of the law, was used to define homicides before and after the change. Main Outcomes and Measures Monthly rates of homicide, firearm-related homicide, suicide, and suicide by firearm in Florida and the 4 comparison states. Results Prior to the stand your ground law, the mean monthly homicide rate in Florida was 0.49 deaths per 100 000 (mean monthly count, 81.93), and the rate of homicide by firearm was 0.29 deaths per 100 000 (mean monthly count, 49.06). Both rates had an underlying trend of 0.1% decrease per month. After accounting for underlying trends, these results estimate that after the law took effect there was an abrupt and sustained increase in the monthly homicide rate of 24.4% (relative risk [RR], 1.24; 95%CI, 1.16-1.33) and in the rate of homicide by firearm of 31.6% (RR, 1.32; 95% CI, 1.21-1.44). No evidence of change was found in the analyses of comparison states for either homicide (RR, 1.06; 95% CI, 0.98-1.13) or homicide by firearm (RR, 1.08; 95% CI, 0.99-1.17). Furthermore, no changes were observed in control outcomes such as suicide (RR, 0.99; 95% CI, 0.94-1.05) and suicide by firearm (RR, 0.98; 95% CI, 0.91-1.06) in Florida between 2005 and 2014. Conclusions and Relevance The implementation of Florida’s stand your ground self-defense law was associated with a significant increase in homicides and homicides by firearm but no change in rates of suicide or suicide by firearm.

[1]  Richard A. Berk,et al.  Applied Time Series Analysis for the Social Sciences , 1980 .

[2]  David Gunnell,et al.  Impact of 2008 global economic crisis on suicide: time trend study in 54 countries , 2013, BMJ : British Medical Journal.

[3]  T. Cook,et al.  Quasi-experimentation: Design & analysis issues for field settings , 1979 .

[4]  Ling Ren,et al.  The Deterrent Effect of the Castle Doctrine Law on Burglary in Texas , 2015 .

[5]  The economic downturn probably reduced violence far more than licensing restrictions. , 2015, Addiction.

[6]  M. Gius.  The relationship between stand-your-ground laws and crime: A state-level analysis , 2016 .

[7]  B. Carr,et al.  The impact of economic austerity and prosperity events on suicide in Greece: a 30-year interrupted time-series analysis , 2015, BMJ Open.

[8]  Euel W. Elliott,et al.  The State of the Castle , 2009 .

[9]  Katherine E Henson,et al.  Risk of Suicide After Cancer Diagnosis in England , 2018, JAMA psychiatry.

[10]  学 赤沢,et al.  Interrupted Time-series Analysis , 2015 .

[11]  Mark Hoekstra,et al.  Does Strengthening Self-Defense Law Deter Crime or Escalate Violence?: Evidence from Expansions to Castle Doctrine , 2013 .

[12]  C. Light.  From a Duty to Retreat to Stand Your Ground , 2015 .

[13]  A. Gasparrini,et al.  The effect of the late 2000s financial crisis on suicides in Spain: an interrupted time-series analysis. , 2013, European journal of public health.

[14]  A K Wagner,et al.  Segmented regression analysis of interrupted time series studies in medication use research , 2002, Journal of clinical pharmacy and therapeutics.

[15]  Douglas J. Wiebe,et al.  Evaluating the Impact of Flexible Alcohol Trading Hours on Violence: An Interrupted Time Series Analysis , 2013, PloS one.

[16]  Marcello Pagano,et al.  Race, law, and health: Examination of 'Stand Your Ground' and defendant convictions in Florida. , 2015, Social science & medicine.

[17]  Liquor licensing or confounding events? Further questions about the interpretations of Menéndez et al. (2015). , 2016, Addiction.

[18]  W. Shadish,et al.  Experimental and Quasi-Experimental Designs for Generalized Causal Inference , 2001 .

[19]  A. Gasparrini,et al.  Interrupted time series regression for the evaluation of public health interventions: a tutorial , 2016, International journal of epidemiology.

[20]  D. Andrews.  Heteroskedasticity and Autocorrelation Consistent Covariance Matrix Estimation , 1991 .

[21]  Steven Pinker,et al.  The better angels of our nature : a history of violence and humanity , 2012 .

[22]  Chris L. S. Coryn,et al.  Using nonequivalent dependent variables to reduce internal validity threats in quasi‐experiments: Rationale, history, and examples from practice , 2011 .

[23]  C. McClellan,et al.  Stand Your Ground Laws, Homicides, and Injuries , 2012, The Journal of Human Resources.

[24]  Mitchell B. Chamlin.  An assessment of the intended and unintended consequences of Arizona's Self-Defense, Home Protection Act , 2014 .

[25]  K. Bhaskaran,et al.  Time series regression studies in environmental epidemiology , 2013, International journal of epidemiology.